1. Field of the Invention
The present invention relates to a structure of a roll-rod for a subframe, and more particularly, to a structure of a roll-rod for a subframe that can more efficiently absorb and damp impact by variably controlling a flow state of a hydro liquid depending on an applied load while alleviating vibration and supporting behavior of a power train by using flow of the hydro liquid filled therein.
2. Description of Related Art
A monocoque body having a small weight and high productivity is primarily used in vehicles, instead of a frame body. In the monocoque body as a structure in which an additional frame is deleted, a power train in which an engine and a transmission are joined to each other is mounted directly on an engine room of a vehicle body. Therefore, in the monocoque body, the vehicle body itself serves as a frame, such that a suspension and chassis parts are respectively mounted thereon, however, a subframe is mounted under a vehicle in order to prevent vibration of the power train from being transferred directly to the vehicle body and to disperse impact when the vehicle collides.
Meanwhile, a supporting method of the power train can be largely divided into an inertia supporting method, a center supporting method, and a hybrid supporting method and among them, the subframe is mounted in the inertia supporting method. As the inertia supporting method, 4-point inertia supporting and 3-point inertia supporting are widely adopted. Therebetween, while as the subframe used in the inertia supporting method, an “I”-shaped subframe so called a dog bone type is used, and a suspension device and a steering device are joined to the subframe and connected to the bottom of the power train through a roll-rod.
That is, as shown in FIG. 1A, while an engine mount and a transmission mount are mounted at both sides of the vehicle body, respectively to support a load of the power train, the roll-rod is mounted on a subframe (not shown) to share displacement control and vibration alleviation of the power train.
A detailed structure of the roll-rod in the related art is shown in FIG. 1B. Referring to FIG. 1B, the roll-rod includes: a bracket bar having a cylindrical front bush mounted on one end thereof, which is connected to the bottom of a power train; an endplate joined to the other end of the bracket bar with a fixation bolt and a fixation nut; a housing joined to slide on the bracket bar and fixed to a subframe; and a rear bush including a first bush disposed at a front side of the housing and a second bush disposed at a rear side of the housing (based on a vehicle).
The first bush and the second bush are made of rubber and isolatedly disposed by a wall surface formed inside the housing. Therefore, while the housing is mounted and fixed on the subframe, the first bush or the second bush behaves to be elastically transformed and restored as the bracket bar and the endplate move.
That is, when the vehicle moves forward, the second bush is compressed by displacement of the power train by inertia to perform a damping function and when the vehicle moves backward or decelerates, the first bush is compressed to perform the damping function.
As described above, the roll-rod that performs load supporting and vibration alleviating functions of the power train occupies a large part in noise, vibration, and harshness (NVH) performance in particular, according to a shape and a characteristic of a rear bush.
However, the rear bush in the related art using elastic force of a material has a problem in that dynamic ratio (an increase ratio of dynamic load to static load) is large and tuning is difficult (in order to meet design requirements).
Further, the elastic transformation and restoration of the rear bush cause a fatigue of a material and durability deteriorates in continuous use as a structure without an additional stopper (supporting to prevent elastic compression of a predetermined reference or more).
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.